Post-temperable nanocrystal electrochromic devices

ABSTRACT

An electrochromic device may include a working electrode that includes a high temperature stable material and nanoparticles of an active core material, a counter electrode, and an electrolyte deposited between the working electrode and the counter electrode. The high temperature stable material may prevent fusing of the nanoparticles of the active core material at temperatures up to 700° C. The high temperature stable material may include tantalum oxide. The high temperature stable material may form a spherical shell or a matrix around the nanoparticles of the active core material. A method of forming an electrochromic device may include depositing a working electrode onto a first substrate, in which the working electrode comprises a high temperature stable material and nanoparticles of an active core material, and heat tempering the working electrode and the first substrate.

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/079,850, filed Nov. 14, 2014, and U.S.Provisional Patent Application No. 62/203,679, filed Aug. 11, 2015, theentire contents of which are incorporated herein by reference.

FIELD

The present invention is generally directed to electrochromic devices,and more particularly to particular nanocrystalline materials andprocess conditions that allow thermally-cured electrodes to be subjectedto tempering conditions.

BACKGROUND OF THE INVENTION

Residential and commercial buildings represent a prime opportunity toimprove energy efficiency and sustainability in the United States. Thebuildings sector alone accounts for 40% of the United States' yearlyenergy consumption (40 quadrillion BTUs, or “quads”, out of 100 total),and 8% of the world's energy use. Lighting and thermal management eachrepresent about 30% of the energy used within a typical building, whichcorresponds to around twelve quads each of yearly energy consumption inthe US. Windows cover an estimated area of about 2,500 square km in theUS and are a critical component of building energy efficiency as theystrongly affect the amount of natural light and solar gain that enters abuilding. Recent progress has been made toward improving window energyefficiency through the use of inexpensive static coatings that eitherretain heat in cold climates (low emissive films) or reject solar heatgain in warm climates (near-infrared rejection films).

Currently, static window coatings can be manufactured at relatively lowcost. However, these window coatings are static and not well suited forlocations with varying climates. An electrochromic (EC) window coatingovercomes these limitations by enhancing the window performance in allclimates. EC window coatings undergo a reversible change in opticalproperties when driven by an applied potential. Some EC devices mayinclude a working electrode, a solid state electrolyte, and a counterelectrode sandwiched between two transparent conductor layers and anouter glass layer. The working electrode may include nanocrystallinestructures or amorphous metal oxide nanoparticles such as WO₃,CS_(x)WO₃, NbO_(x), TiO₂, MoO₃, NiO₂, and V₂O₅.

As part of the EC device fabrication process, the working electrode,solid state electrolyte, and counter electrode may be exposed to hightemperatures as part of a tempering or heat quench process. For example,the EC device layers may be exposed to temperatures of 650° C. orhigher. At these temperatures, some of the layers of the EC device, andin particular the working electrode, may undergo sintering or otherundesirable crystallization changes or phase transitions. These changesmay affect the operation or efficiency of the EC device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are schematic representations of electrochromic devicesaccording to various embodiments.

FIGS. 2A-2D are SEM images of crystalline nanostructures that may beused in working electrodes of an electrochromic device before and aftertempering.

FIGS. 3A-3B are SEM images of crystalline nanostructures that may beused in counter electrodes of an electrochromic device before and aftertempering.

FIG. 3C are images of a counter electrode in bright and dark modes afterundergoing tempering.

FIGS. 3D-3E are SEM images of alternative crystalline nanostructuresthat may be used in counter electrodes of an electrochromic devicebefore and after tempering.

FIGS. 4A-4B are diagrams of high temperature stable materialssurrounding nanoparticles according to various embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments disclosed herein provide electrochromicnanostructured materials capable of selectively modulating radiation innear-infrared (NIR) and visible spectral regions. The material mayinclude nanostructured doped transition metal oxides with ternarycompounds of the type A_(x)M_(z)O_(y). In various embodimentA_(x)M_(z)O_(y) compounds, if it is assumed that z=1, then 0.08≦x≦0.5(preferably 0.25≦x≦0.35), and 2≦y≦3. In various embodiments, since thenanostructures may be non-uniform as a function of depth, x mayrepresent an average doping content. To operate, the subject materialmay be fabricated into an electrode that will change optical propertiesafter driven by an applied voltage.

In order to improve the performance of EC window coatings, selectivemodulation of NIR and visible spectra radiation, and avoidance ofdegrading effects of UV radiation, may be desired. Various embodimentsmay provide single-component electrochromic nanostructured materialscapable of selectively modulating NIR and visible spectral regions.Further, since certain spectral regions may damage the electrochromicnanostructured material, the various embodiments may incorporate atleast one protective material and/or protective layer to prevent suchdamage.

The various embodiments provide devices and methods for enhancingoptical changes in windows using electrochromic nanostructured materialsfabricated into an electrode to form an electrochromic device. Invarious embodiments, the material may undergo a reversible change inoptical properties when driven by an applied potential. Based on theapplied potential, the electrochromic nanostructured materials maymodulate NIR radiation (wavelength of around 780-2500 nm), as well asvisible radiation (wavelength of around 400-780 nm). In an example, thedevice may include a first nanostructured material that modulatesradiation in a portion of the NIR spectral region and in the visiblespectral region, and a second nanostructured material that modulatesradiation in an overlapping portion of the NIR spectral region such thatthe NIR radiation modulated by the device as a whole is enhanced andexpanded relative to that of just the first nanostructured material. Invarious embodiments, the material may operate in multiple selectivemodes based on the applied potential.

Further, the various embodiments may include at least one protectivematerial to prevent or reduce damage to an electrochromic nanostructuredmaterial that may result from repeated exposure to radiation in the UVspectral region. In an example, a protective material may be used toform at least one barrier layer in the device that is positioned toblock UV radiation from reaching the first nanostructured material andelectrolyte. In another example, a protective material may be used toform a layer that is positioned to block free electron or hole chargecarriers created in the electrolyte due to absorption of UV radiation bythe nanostructured electrode material from migrating to that material,while allowing conduction of ions from the electrolyte (i.e., anelectron barrier and ion conductor).

In various embodiments, control of individual operating modes formodulating absorption/transmittance of radiation in specific spectralregions may occur at different applied biases. Such control may provideusers with the capability to achieve thermal management within buildingsand other enclosures (e.g., vehicles, etc.), while still providingshading when desired.

FIGS. 1A-1C illustrate embodiment electrochromic devices. It should benoted that such electrochromic devices may be oriented upside down orsideways from the orientations illustrated in FIGS. 1A-1C. Furthermore,the thickness of the layers and/or size of the components of the devicesin FIGS. 1A-1C are not drawn to scale or in actual proportion to oneanother other, but rather are shown as representations.

In FIG. 1A, an embodiment electrochromic device 100 may include a firsttransparent conductor layer 102 a, a working electrode 104, a solidstate electrolyte 106, a counter electrode 108, and a second transparentconductor layer 102 b. Some embodiment electrochromic devices may alsoinclude one or more optically transparent support layer, such as plasticor glass layer 110 positioned in front of the first transparentconductor layer 102 a and/or positioned behind the second transparentconductor layer 102 b.

The first and second transparent conductor layers 102 a, 102 b may beformed from transparent conducting films fabricated using inorganicand/or organic materials. For example, the transparent conductor layers102 a, 102 b may include inorganic films of transparent conducting oxide(TCO) materials, such as indium tin oxide (ITO) or fluorine doped tinoxide (FTO). In other examples, organic films in transparent conductorlayers 102 a, 102 b may include graphene and/or various polymers.

In the various embodiments, the working electrode 104 may includenanostructures 112 of a doped transition metal oxide bronze, andoptionally nanostructures 113 of a transparent conducting oxide (TCO)composition shown schematically as circles and hexagons for illustrationpurposes only. As discussed above, the thickness of the layers of thedevice 100, including and the shape, size and scale of nanostructures isnot drawn to scale or in actual proportion to each other, but isrepresented for clarity. In the various embodiments, nanostructures 112,113 may be embedded in an optically transparent matrix material orprovided as a packed or loose layer of nanostructures exposed to theelectrolyte.

In the various embodiments, the doped transition metal oxide bronze ofnanostructures 112 may be a ternary composition of the type AxMzOy,where M represents a transition metal ion species in at least onetransition metal oxide, and A represents at least one dopant. Transitionmetal oxides that may be used in the various embodiments include, butare not limited to any transition metal oxide which can be reduced andhas multiple oxidation states, such as niobium oxide, tungsten oxide,molybdenum oxide, vanadium oxide, titanium oxide and mixtures of two ormore thereof. In one example, the nanostructured transition metal oxidebronze may include a plurality of tungsten oxide (WO_(3−x))nanoparticles, where 0≦x≦0.33, such as 0≦x≦0.1.

In various embodiments, the at least one dopant species may be a firstdopant species that, upon application of a particular first voltagerange, causes a first optical response. The applied voltage may be, forexample, a negative bias voltage. Specifically, the first dopant speciesmay cause a surface plasmon resonance effect on the transition metaloxide by creating a significant population of delocalized electroniccarriers. Such surface plasmon resonance may cause absorption of NIRradiation at wavelengths of around 780-2000 nm, with a peak absorbanceat around 1200 nm. In various embodiments, the specific absorbances atdifferent wavelengths may be varied/adjusted based other factors (e.g.,nanostructure shape, size, etc.), discussed in further detail below. Inthe various embodiments, the first dopant species may be an ion speciesselected from the group of cesium, rubidium, and lanthanides (e.g.,cerium, lanthanum, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, and lutetium).

In various embodiments, the dopant may include a second dopant speciesthat causes a second optical response based upon application of avoltage within a different, second particular range. The applied voltagemay be, for example, a negative bias voltage. In an embodiment, thesecond dopant species may migrate between the solid state electrolyte106 and the nanostructured transition metal oxide bronze of the workingelectrode 104 as a result of the applied voltage. Specifically, theapplication of voltage within the particular range may cause the seconddopant species to intercalate and deintercalate the transition metaloxide structure. In this manner, the second dopant may cause a change inthe oxidation state of the transition metal oxide, which may cause apolaron effect and a shift in the lattice structure of the transitionmetal oxide. This shift may cause absorption of visible radiation, forexample, at wavelengths of around 400-780 nm.

In various embodiments, the second dopant species may be anintercalation ion species selected from the group of lanthanides (e.g.,cerium, lanthanum, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, and lutetium), alkali metals (e.g., lithium, sodium,potassium, rubidium, and cesium), and alkali earth metals (e.g.,beryllium, magnesium, calcium, strontium, and barium). In otherembodiments, the second dopant species may include a charged protonspecies.

In various embodiments, nanostructures 113 may optionally be mixed withthe doped transition metal oxide bronze nanostructures 112 in theworking electrode 104. In the various embodiments, the nanostructures113 may include at least one TCO composition, which prevents UVradiation from reaching the electrolyte and generating electrons. In anexample embodiment, the nanostructures 113 may include an indium tinoxide (ITO) composition, which may be a solid solution of around 60-95wt % (e.g., 85-90 wt %) indium(III) oxide (In₂O₃) and around 5-40 wt %(e.g., 10-15 wt %) tin(IV) oxide (SnO₂). In another example embodiment,the nanostructures 113 may include an aluminum-doped zinc oxide (AZO)composition, which may be a solid solution of around 99 wt % zinc oxide(ZnO) and around 2 wt % aluminum(III) oxide (Al₂O₃). Additional oralternative TCO compositions that may be used to form nanostructures 113in the various embodiments include, but are not limited to, indiumoxide, zinc oxide and other doped zinc oxides such as gallium-doped zincoxide and indium-doped zinc oxide.

The TCO composition of nanostructures 113 may be transparent to visiblelight and, upon application of the first voltage, may modulateabsorption of NIR radiation at wavelengths of around 1200-2500 nm, withpeak absorbance around 2000 nm (e.g., at a longer peak wavelength thanthe bronze nanoparticles 112, but with overlapping absorption bands). Inparticular, application of the first voltage may cause an increase infree electron charge carriers, and therefore cause a surface plasmonresonance effect in at least one TCO composition of nanostructures 113.In an embodiment in which the TCO composition is ITO, the surfaceplasmon resonance effect may be caused by oscillation of free electronsproduced by the replacement of indium ions (In³⁺) with tin ions (Sn⁴⁺).Similar to the transition metal oxide bronze, such surface plasmonresonance may cause a change in absorption properties of the TCOmaterial. In some embodiments, the change in absorption properties maybe an increase in absorbance of NIR radiation at wavelengths thatoverlaps with that of the nanostructures 112. Therefore, the addition ofTCO composition nanostructures 113 to the working electrode 104 mayserve to expand the range of NIR radiation absorbed (e.g., atwavelengths of around 780-2500 nm) compared to that of thenanostructures 112 alone (e.g., at wavelengths of around 780-2000 nm),and to enhance absorption of some of that NIR radiation (e.g., atwavelengths of around 1200-2000 nm).

Based on these optical effects, the nanostructure 112 and optionalnanostructure 113 of the working electrode may progressively modulatetransmittance of NIR and visible radiation as a function of appliedvoltage by operating in at least three different modes. For example, afirst mode may be a highly solar transparent (“bright”) mode in whichthe working electrode 104 is transparent to NIR radiation and visiblelight radiation. A second mode may be a selective-IR blocking (“cool”)mode in which the working electrode 104 is transparent to visible lightradiation but absorbs NIR radiation. A third mode may be a visibleblocking (“dark”) mode in which the working electrode 104 absorbsradiation in the visible spectral region and at least a portion of theNIR spectral region. In an example, application of a first voltagehaving a negative bias may cause the electrochromic device to operate inthe cool mode, blocking transmittance of NIR radiation at wavelengths ofaround 780-2500 nm. In another example, application of a second negativebias voltage having a higher absolute value than the first voltage maycause the electrochromic device to operate in the dark state, blockingtransmittance of visible radiation (e.g., at wavelengths of around400-780 nm) and NIR radiation at wavelengths of around 780-1200 nm. Inanother example, application of a third voltage having a positive biasmay cause the electrochromic device to operate in the bright state,allowing transmittance of radiation in both the visible and NIR spectralregions. In various embodiments, the applied voltage may be between −5Vand 5V, preferably between −2V and 2V. For example, the first voltagemay be −0.25V to −0.75V, and the second voltage may be −1V to −2V. Inanother example, the absorbance of radiation at a wavelength of 800-1500nm by the electrochromic device may be at least 50% greater than itsabsorbance of radiation at a wavelength of 450-600 nm.

Alternatively, the nanostructure 112 and optional nanostructure 113 ofthe working electrode may modulate transmittance of NIR and visibleradiation as a function of applied voltage by operating in two differentmodes. For example, a first mode may be a highly solar transparent(“bright”) mode in which the working electrode 104 is transparent to NIRradiation and visible light radiation. A second mode may be a visibleblocking (“dark”) mode in which the working electrode 104 absorbsradiation in the visible spectral region and at least a portion of theNIR spectral region. In an example, application of a first voltagehaving a negative bias may cause the electrochromic device to operate inthe dark mode, blocking transmittance of visible and NIR radiation atwavelengths of around 780-2500 nm. In another example, application of asecond voltage having a positive bias may cause the electrochromicdevice to operate in the bright mode, allowing transmittance ofradiation in both the visible and NIR spectral regions. In variousembodiments, the applied voltage may be between −2V and 2V. For example,the first voltage may be −2V, and the second voltage may be 2V.

In various embodiments, the solid state electrolyte 106 may include atleast a polymer material and a plasticizer material, such thatelectrolyte may permeate into crevices between the transition metaloxide bronze nanoparticles 112 (and/or nanoparticles 113 if present).The term “solid state,” as used herein with respect to the electrolyte106, refers to a polymer-gel and/or any other non-liquid material. Insome embodiments, the solid state electrolyte 106 may further include asalt containing, for example, an ion species selected from the group oflanthanides (e.g., cerium, lanthanum, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, and lutetium), alkali metals (e.g.,lithium, sodium, potassium, rubidium, and cesium), and alkali earthmetals (e.g., beryllium, magnesium, calcium, strontium, and barium). Inan example embodiment, such salt in the solid state electrolyte 106 maycontain a lithium and/or sodium ions. In some embodiments, the solidstate electrolyte 106 may initially contain a solvent, such as butanol,which may be evaporated off once the electrochromic device is assembled.In some embodiments, the solid state electrolyte 106 may be around 40-60wt % plasticizer material, preferably around 50-55 wt % plasticizermaterial. In an embodiment, the plasticizer material may include atleast one of tetraglyme and an alkyl hydroperoxide. In an embodiment,the polymer material of the solid state electrolyte 106 may bepolyvinylbutyral (PVB), and the salt may be lithiumbis(trifluoromethane). In other embodiments, the solid state electrolyte106 may include at least one of lithium phosphorus oxynitride (LiPON)and tantalum pentoxide (Ta₂O₅).

In some embodiments, the electrolyte 106 may include a sacrificial redoxagent (SRA). Suitable classes of SRAs may include, but are not limitedto, alcohols, nitrogen heterocycles, alkenes, and functionalizedhydrobenzenes. Specific examples of suitable SRAs may include benzylalcohol, 4-methylbenzyl alcohol, 4-methoxybenzyl alcohol, dimethylbenzylalcohol (3,5-dimethylbenzyl alcohol, 2,4-dimethylbenzyl alcohol etc.),other substituted benzyl alcohols, indoline,1,2,3,4-tetrahydrocarbazole, N,N-dimethylaniline, 2,5-dihydroanisole,etc. In various embodiments, the SRA molecules may create an air stablelayer that does not require an inert environment to maintain charge.

Polymers that may be part of the electrolyte 106 may include, but arenot limited to, poly(methyl methacrylate) (PMMA), poly(vinylbutyral-co-vinyl alcohol-co-vinyl acetate) (PVB), poly(ethylene oxide)(PEO), fluorinated co-polymers such as poly(vinylidenefluoride-co-hexafluoropropylene), poly(acrylonitrile) (PAN), poly(vinylalcohol) (PVA), etc. Plasticizers that may be part of the polymerelectrolyte formulation include, but are not limited to, glymes(tetraglyme, triglyme, diglyme etc.), propylene carbonate, ethylenecarbonate, ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate,1-butyl-3-methylimidazolium hexafluorophosphate,1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide,1-butyl-1-methyl-pyrrolidinium bis(trifluoromethane sulfonyl)imide,etc.), N,N-dimethylacetamide, and mixtures thereof.

In some embodiments, the electrolyte 106 may include, by weight, 10-30%polymer, 40-80% plasticizer, 5-25% lithium salt, and 0.5-10% SRA.

The counter electrode 108 of the various embodiments should be capableof storing enough charge to sufficiently balance the charge needed tocause visible tinting to the nanostructured transition metal oxidebronze in the working electrode 104. In various embodiments, the counterelectrode 108 may be formed as a conventional, single component film, ananostructured film, or a nanocomposite layer.

In some embodiments, the counter electrode 108 may be formed from atleast one passive material that is optically transparent to both visibleand NIR radiation during the applied biases. Examples of such passivecounter electrode materials may include CeO₂, CeVO₂, TiO₂, indium tinoxide, indium oxide, tin oxide, manganese or antimony doped tin oxide,aluminum doped zinc oxide, zinc oxide, gallium zinc oxide, indiumgallium zinc oxide, molybdenum doped indium oxide, Fe₂O₃, and/or V₂O₅.In other embodiments the counter electrode 108 may be formed from atleast one complementary material, which may be transparent to NIRradiation but which may be oxidized in response to application of abias, thereby causing absorption of visible light radiation. Examples ofsuch complementary counter electrode materials may include Cr₂O3, MnO₂,FeO₂, CoO₂, NiO₂, RhO₂, or IrO₂. The counter electrode materials mayinclude a mixture of one or more passive materials and/or one or morecomplementary materials described above.

Without being bound to any particular theory, it is believed that theapplication of a first voltage in the various embodiments may cause theinterstitial dopant species (e.g., cesium) in the crystal structure ofthe transition metal oxide bronze to have a greater amount of freecarrier electrons and/or to cause the interstitial dopant species (e.g.,lithium ions from the electrolyte) to perform non-faradaic capacitive orpseudo-capacitive charge transfer on the surface of the nanostructures112, which may cause the surface plasmon resonance effect to increasethe absorption of NIR radiation. In this manner, the absorptionproperties of the transition metal oxide bronze characteristics maychange (i.e., increased absorption of NIR radiation) upon application ofthe first voltage. Further, application of a second voltage having ahigher absolute value than the first voltage in the various embodimentsmay cause faradaic intercalation of an intercalation dopant species(e.g., lithium ions) from the electrolyte into the transition metaloxide nanostructures. It is believed that the interaction of this dopantspecies provides interstitial dopant atoms in the lattice which createsa polaron effect. In this manner, the lattice structure of transitionmetal oxide nanoparticles may experience a polaron-type shift, therebyaltering its absorption characteristics (i.e., shift to visibleradiation) to block both visible and near infrared radiation.

In some embodiments, in response to radiation of certain spectralregions, such as UV (e.g., at wavelengths of around 10-400 nm) may causeexcitons to be generated in the polymer material of the solid stateelectrolyte 106. The UV radiation may also excite electrons in the dopedtransition metal oxide bronze to move into the conduction band, leavingholes in the valence band. The generated excitons in the polymermaterial may dissociate to free carriers, the electrons of which may beattracted to the holes in the valence band in the doped transition metaloxide bronze (e.g., cesium-doped tungsten trioxide (Cs_(x)WO₃)) ofnanoparticles 112. Since electrochemical reduction of various transitionmetal oxide bronzes by such free electron charge carriers may degradetheir performance (i.e., from unwanted coloration of the transitionmetal oxide bronze), embodiment devices may include one or more layer ofa protective material to prevent UV radiation from reaching the solidstate electrolyte 106, in addition to or instead of nanostructures 113mixed into the working electrode.

FIG. 1B illustrates an embodiment electrochromic device 150 thataddresses degradation of the doped transition metal oxide bronzenanostructures 112. Similar to device 100 shown in FIG. 1A, device 150may include a first transparent conductor layer 102 a, a workingelectrode 104, a solid state electrolyte 106, a counter electrode 108, asecond transparent conductor layer 102 b, and one or more opticallytransparent support layers 110. In addition, device 150 may include oneor more protective layers 116 a, 116 b made of a material that absorbsUV radiation. In an example embodiment, the UV protective layer 116 amay be placed between the transparent conductor 102 a and the glass 110on one side of the device 150, while the UV protective layer 116 b maybe placed between the transparent conductor 102 b and the glass on theother side of the device 150. Alternatively, the device 150 may includea first protective layer 116 a positioned in front of the firsttransparent conductor layer 102 a. For example, the first protectivelayer 116 a may be positioned between the first transparent conductorlayer 102 a and, if present, the optically transparent support layer110. Alternatively, if present, the first protective layer 116 may bepositioned in front of the optically transparent support layer 110(i.e., on the side of the conductor layer 102 a or support layer 110opposite from the working electrode 104). In another example embodiment,the device 150 may additionally or alternatively provide a secondprotective layer 116 b that is positioned between the first transparentconductor layer 102 a and the working electrode 104.

The UV radiation absorbing material of the one or more protective layers116 a, 116 b of the various embodiments may be any of a number ofbarrier films. For example, the one or more protective layer 116 a maybe a thin film of at least one TCO material, which may include a same asor different from TCO compositions in the nanostructures 113. In anexample embodiment, a protective layer 116 a of the device 150 may be anITO thin film, and therefore capable of absorbing UV radiation byband-to-band absorption (i.e., absorption of a UV photon providingenough energy to excite an electron from the valence band to theconduction band). In another example embodiment, the device may includethe TCO nanostructures 113 made of ITO, as well as a protective layer116 a composed of an ITO thin film. Alternatively, the TCOnanostructures 113 may form a separate thin film layer 116 b disposedbetween the transition metal oxide bronze nanoparticles 112 and thetransparent conductor 102 a. In some embodiments, the UV radiationabsorbing materials of protective layers 116 a, 116 b may includeorganic or inorganic laminates.

In another embodiment, at least one UV protective layer, such asprotective layer 116 a in FIG. 1B, may be a UV radiation reflector madeof a high index transparent metal oxide. Since birds can see radiationin the UV range, a UV reflector may be implemented in embodimentspositioned as outside windows in order to prevent birds from hitting thewindows. In some other embodiments, UV radiation absorbing organicmolecules and/or inorganic UV radiation absorbing nanoparticles (e.g.,zinc oxide, indium oxide, ITO, etc.) may be incorporated within theelectrolyte 106 material.

FIG. 1C illustrates another embodiment electrochromic device 170 thataddresses degradation of the doped transition metal oxide bronzenanostructures 112 by controlling the effects of the electron chargecarriers generated in the electrolyte from exposure to UV radiation.Similar to devices 100 and 150 discussed above with respect to FIGS. 1Aand 1B respectively, device 170 may include a first transparentconductor layer 102 a, a working electrode 104, a solid stateelectrolyte 106, a counter electrode 108, a second transparent conductorlayer 102 b, and one or more optically transparent support layer 110. Inaddition, device 170 may include a protective layer 118 positionedbetween the working electrode 104 and the electrolyte 106. Theprotective layer 118 may be composed of one or more ionically conductiveand electrically insulating material.

As discussed above, without being bound to any particular theory, it isbelieved that the migration of intercalation ions between theelectrolyte 106 and the working electrode 104 is responsible for atleast some of the device's capability to modulate spectral absorption.Therefore, in order to maintain operability of the device, theelectrically insulating material used to form the protective layer 118should also be ionically conductive. That is, the material of theprotective layer 118 may prevent or reduce free electrons in the solidstate electrolyte layer 106 from reducing the transition oxide bronze ofnanoparticles 112, while allowing the diffusion of ions of anintercalation dopant species (e.g., Na, Li, etc.) between theelectrolyte 106 and working electrode 104. In an example embodiment, theelectrically insulating material that makes up the protective layer 118may be tantalum oxide, such as tantalum pentoxide (Ta₂O₅), which blocksmigration of electrons from the electrolyte 106 while allowing diffusionof the intercalation dopant species ions (e.g., lithium ions) from theelectrolyte 106. In this manner, degradation of the transition metaloxide bronze is reduced or prevented by controlling the effect of theabsorbed UV radiation in addition to or instead of instead of blockingits absorption. Other example materials that may be used to form theprotective layer 118 in addition to or instead of tantalum pentoxide mayinclude, without limitation, strontium titanate (SrTiO₃), zirconiumdioxide (ZrO₂), indium oxide, zinc oxide, tantalum carbide, niobiumoxide, and various other dielectric ceramics having similar electricaland/or crystalline properties to tantalum pentoxide.

In an alternative embodiment, instead of or in addition to theprotective layer 118, the nanostructures 112 may each be encapsulated ina shell containing an electrically insulating and ionically conductivematerial, which may be the same as or different from the material of theprotective layer 118 (e.g., tantalum oxide, strontium titanate, zincoxide, indium oxide, zirconium oxide, tantalum carbide, or niobiumoxide).

In an example embodiment, each nanostructure 112 may have a core ofcubic or hexagonal unit cell lattice structure tungsten bronze,surrounded by a shell of tantalum pentoxide.

In some embodiments, the electrolyte 106 may include a polymer thatreduces damage to the device due to UV radiation. The polymer may be anyof a number of polymers that are stable upon absorption of UV radiation(e.g., no creation of proton/electron pairs). Examples of such polymersmay include, but are not limited to, fluorinated polymers withouthydroxyl (—OH) groups (e.g., polyvinylidene difluoride (PVDF)).

In another embodiment, a positive bias may be applied to the counterelectrode 108 to draw UV radiation generated electrons from theelectrolyte 106 to the counter electrode 108 in order to reduce orprevent electrons from the electrolyte 106 from moving to the workingelectrode 104 to avoid the free electron-caused coloration of the dopedtransition metal oxide bronze in the working electrode 104.

In another embodiment, a device may include more than one of, such asany two of, any three of, or all four of: (i) a protective layer ofelectrically insulating material (e.g., protective layer 118 orprotective material shells around the bronze nanoparticles), (ii) one ormore protective layer of UV radiation absorbing material (e.g.,protective layer(s) 116 a and/or 116 b in FIG. 1B and/or UV radiationabsorbing organic molecules and/or inorganic UV radiation absorbingnanoparticles incorporated within the electrolyte 106 material), (iii)electrolyte polymer that is stable upon absorption of UV radiation,and/or (iv) application of positive bias to the counter electrode 108.In various embodiments, the nanostructures 113 may be included in oromitted from electrochromic devices 150, 170.

In another embodiment, the protective layer(s) 116 a and/or 116 b maycomprise a stack of metal oxide layers. Alternatively, the stack maycomprise a separate component that is provided instead of or in additionto the layer(s) 116 a and/or 116 b. The stack may provide improvement inthe reflected color of the electrochromic device. Prior art devicesgenerally have a reddish/purplish color when viewed in reflection. Thestack may comprise index-matched layers between the glass andtransparent conductive oxide layer to avoid the reddish/purplishreflected color. As noted above, the index-matched layer can serve asthe UV absorber or be used in addition to another UV absorber. The stackmay comprise a zinc oxide based layer (e.g., ZnO or AZO) beneath anindium oxide based layer (e.g., indium oxide or ITO).

Compared to nanocomposite electrochromic films, the various embodimentsmay involve similar production by utilizing a single nanostructuredmaterial in the working electrode to achieve the desired spectralabsorption control in both NIR and visible regions, and anothernanostructured material to enhance and expand such control in the NIRregion. Further, the various embodiments may provide one or moreadditional layer(s) of a protective material to minimize degradation ofthe single nanostructured material.

In some embodiments, the working electrode and/or the counter electrodemay additionally include at least one material, such as an amorphousnano structured material, that enhances spectral absorption in the lowerwavelength range of the visible region. In some embodiments, the atleast one amorphous nanostructured material may be at least onenanostructured amorphous transition metal oxide.

In particular, the amorphous nano structured materials may provide colorbalancing to the visible light absorption that may occur due to thepolaron-type shift in the spectral absorption of the doped-transitionmetal oxide bronze. As discussed above, upon application of the secondvoltage having a higher absolute value, the transition metal oxidebronze may block (i.e., absorb) radiation in the visible range. Invarious embodiments, the absorbed visible radiation may have wavelengthsin the upper visible wavelength range (e.g., 500-700 nm), which maycause the darkened layer to appear blue/violet corresponding to theun-absorbed lower visible wavelength range (e.g., around 400-500 nm). Invarious embodiments, upon application of the second voltage, the atleast one nanostructured amorphous transition metal oxide may absorbcomplementary visible radiation in the lower visible wavelength range(e.g., 400-500 nm), thereby providing a more even and complete darkeningacross the visible spectrum with application of the second voltage. Thatis, use of the amorphous nanostructured material may cause the darkenedlayer to appear black.

In some embodiments, at least one nanostructured amorphous transitionmetal oxide may be included in the working electrode 104 in addition tothe doped-transition metal oxide bronze nanostructures 112 and theoptional TCO nanostructures 113. An example of such material in theworking electrode 104 may be, but is not limited to, nanostructuredamorphous niobium oxide, such as niobium(II) monoxide (NbO) or otherniobium oxide materials (e.g., NbO_(x)). In some embodiments, thecounter electrode 108 may include, as a complementary material, at leastone nanostructured amorphous transition metal oxide. That is, inaddition to optically passive materials, the counter electrode 108 mayinclude at least one material for color balancing (i.e., complementing)the visible radiation absorbed in the working electrode (i.e., by thetransition metal oxide bronze. An example of such material in thecounter electrode 108 may be, but is not limited to, nanostructuredamorphous nickel oxide, such as nickel(II) oxide (NiO) or other nickeloxide materials (e.g., NiO_(x)).

In the various embodiments, nanostructures that form the working and/orcounter electrode, including the at least one amorphous nanostructuredmaterial, may be mixed together in a single layer. An example of a mixedlayer is shown in FIG. 1A with respect to transition metal oxide bronzenanostructures 112 and TCO nanostructures 113. Alternatively,nanostructures that form the working and/or counter electrode, includingthe at least one amorphous nanostructured material, may be separatelylayered according to composition. For example, a working electrode mayinclude a layer of amorphous NbO_(x) nanostructures, a layer oftransition metal oxide bronze nanostructures, and a layer of ITOnanostructures, in any of a number of orders.

The nanostructured transition metal oxide bronzes that may be part ofthe working electrode 104 in various embodiment devices can be formedusing any of a number of low cost solution process methodologies. Forexample, solutions of Nb:TiO₂ and Cs_(x)WO₃ may be synthesized usingcolloidal techniques. Compared to other synthetic methodologies,colloidal synthesis may offer a large amount of control over thenanostructure size, shape, and composition of the nanostructuredtransition metal oxide bronze. After deposition, a nanostructuredtransition metal oxide bronze material in the working electrode 104 maybe subjected to a thermal post treatment in air to remove and capligands on the surface of the nanostructures.

In various embodiments, nanostructured amorphous transition metal oxidematerials may be formed at room temperature from an emulsion and anethoxide precursor. For example, procedures used to synthesize tantalumoxide nanoparticles that are described in “Large-scale synthesis ofbioinert tantalum oxide nanoparticles for X-ray computed tomographyimaging and bimodal image-guided sentinel lymph node mapping” by M H Ohet al. (J Am Chem Soc. 2011 Apr. 13; 133(14):5508-15), incorporated byreference herein, may be similarly used to synthesize amorphoustransition metal oxide nanoparticles. For example, an overall syntheticprocess of creating the nanoparticle, as described in Oh et al., mayadopted from the microemulsion synthesis of silica nanoparticles. Insuch process, a mixture of cyclohexane, ethanol, surfactant, and acatalysis for the sol-gel reaction may be emulsified. The ethoxideprecursor may be added to the emulsion, and uniform nanoparticles may beformed by a controlled-sol gel reaction in the reverse micelles at roomtemperature within around 5 minutes. The sol-gel reaction may becatalyzed, for example, by NaOH.

In some embodiments, the nanostructured amorphous transition metal oxidemay be sintered at a temperature of at least 400° C. for at least 30minutes, such as 400 to 600° C. for 30 to 120 minutes to form a porousweb. In an example embodiment, the porous web may be included in aworking electrode 104, with the tungsten bronze nanoparticles and ITOnanoparticles incorporated in/on the web. Alternatively, the sinteringstep may be omitted and the nano structured amorphous transition metaloxide may remain in the device in the form of nanoparticles havingamorphous structure. In this embodiment, the device containing thenanostructured amorphous transition metal oxide may include or may omitthe protective layer(s) 116 a, 116 b, and 118, the UV stable electrolytepolymer, and the application of positive bias to the counter electrode.

Electrochromic responses of prepared nano structured transition metaloxide bronze materials (e.g., Cs_(x)WO₃, Nb:TiO₂, etc.) may bedemonstrated by spectroelectrochemical measurements.

In various embodiments, the shape, size, and doping levels ofnanostructured transition metal oxide bronzes may be tuned to furthercontribute to the spectral response by the device. For instance, the useof rod versus spherical nanostructures 112 may provide a wider level ofporosity, which may enhance the switching kinetics. Further, a differentrange of dynamic plasmonic control may occur for nanostructures withmultiple facets, such as at least 20 facets.

Various embodiments may also involve alternation of the nanostructures112 that form the working electrode 104. For example, the nanostructuresmay be nanoparticles of various shapes, sizes and/or othercharacteristics that may influence the absorption of NIR and/or visiblelight radiation. In some embodiments, the nanostructures 112 may beisohedrons that have multiple facets, preferably at least 20 facets.

In some embodiments, the transition metal oxide bronze nanostructures112 may be a combination of nanoparticles having a cubic unit cellcrystal lattice (“cubic nanoparticles”) and nanoparticles having ahexagonal unit cell crystal lattice (“hexagonal nanoparticles”). Eachunit cell type nanoparticle contributes to the performance of theworking electrode 104. For example, the working electrode 104 mayinclude both cubic and hexagonal cesium doped tungsten oxide bronzenanoparticles. In alternative embodiments, the working electrode 104 mayinclude either cubic or hexagonal cesium doped tungsten oxidenanoparticles. For example, the working electrode 104 may include cubiccesium-doped tungsten oxide (e.g. Cs₁W₂O_(6±X)) nanoparticles andamorphous niobium oxide nanoparticles or hexagonal cesium-doped tungstenoxide (e.g. Cs_(0.29)W₁O₃) nanoparticles without niobium oxide. Inalternative embodiments, the working electrode 104 may include undopedtungsten oxide (e.g. WO_(3−X)) nanoparticles where 0≦X≦0.1.

For example, upon application of the first (i.e., lower absolute value)voltage described above, the hexagonal bronze nanostructures 112 mayblock NIR radiation having wavelengths in the range of around 800-1700nm, with the peak absorption at the mid-NIR wavelength of around 1100nm. The cubic bronze nanostructures 112 may block NIR radiation havingwavelengths in the close-NIR range with the peak absorption of around890 nm. The indium oxide based (including ITO) and/or zinc oxide based(including AZO) nanostructures 113 may be included in the workingelectrode 104 to block the higher wavelength IR radiation uponapplication of the first voltage. Thus, the cubic bronze and hexagonalbronze nanostructures may block respective close and mid-NIR radiation(e.g., using the Plasmon effect), while the nanostructures 113 may blockthe higher wavelength IR radiation.

Upon application of the second (i.e., higher absolute value) voltagedescribed above, the cubic bronze nanostructures 112 may block visibleand NIR radiation having wavelengths in the range of around 500-1500 nm,with the peak absorption at the close-NIR wavelength of around 890 nm(e.g., using the polaron effect). Optionally, the amorphous niobiumoxide may also be added to the working electrode 104 to block the shortwavelength visible radiation (e.g., 400 to 500 nm wavelength).

The cubic bronze nanostructures block visible radiation via the polaroneffect at a lower applied voltage than the hexagonal bronzenanostructures. Thus, the second voltage may have an absolute valuewhich is below the value at which the hexagonal bronze nanostructuresblock visible radiation via the polaron effect such that thesenanostructures do not contribute to blocking of visible radiation.Alternatively, the second voltage may have an absolute value which isabove the value at which the hexagonal bronze nanostructures blockvisible radiation via the polaron effect such that these nanostructuresalso contribute to blocking of visible radiation.

Embodiment nanoparticles that form the working electrode 104 may bearound 4-6 nm in diameter, and may include 40 to 70 wt %, such as around50 wt % cubic tungsten bronze nanostructures, 15 to 35 wt %, such asaround 25 wt % hexagonal tungsten bronze nanostructures, and optionally15 to 35 wt %, such as around 25 wt % ITO nanostructures. In someembodiments, in order to achieve color balancing as described above, thenanoparticles that form the working electrode 104 may optionally includearound 5-10 wt % amorphous NbO_(x) nanostructures in place of cubictungsten bronze nanostructures. In this embodiment, the devicecontaining two types of bronze nanoparticles may include or may omit theprotective layer(s) 116 a, 116 b, and 118, the UV stable electrolytepolymer, the application of positive bias to the counter electrode, andthe amorphous niobium oxide.

In summary, the working electrode 104 may include one or more of thefollowing components:

-   -   (a) metal oxide bronze nanostructures 112 having (i) a        cubic, (ii) hexagonal, or (iii) a combination of cubic and        hexagonal unit cell lattice structure;    -   (b) protective (i) indium oxide based (including ITO) and/or        zinc oxide based (including AZO) nanostructures 113;    -   (c) amorphous niobium oxide nanoparticles and/or web; and/or    -   (d) additional nanostructures selected from undoped tungsten        oxide, molybdenum oxide, titanium oxide, and/or vanadium oxide.

The counter electrode 108 may include one or more of the followingcomponents:

-   -   (a) passive electrode material selected from cerium(IV) oxide        (CeO₂), titanium dioxide (TiO₂), cerium(III) vanadate (CeVO₂),        indium(III) oxide (In₂O₃), tin-doped indium oxide, tin(II) oxide        (SnO₂), manganese-doped tin oxide, antimony-doped tin oxide,        zinc oxide (ZnO), aluminum-doped zinc oxide (AZO), iron(III)        oxide (Fe₂O₃), and vanadium(V) oxide (V₂O₅);    -   (b) an active electrode material selected from chromium(III)        oxide (Cr₂O₃), manganese dioxide (MnO₂), iron(II) oxide (FeO),        cobalt oxide (CoO), nickel(II) oxide (NiO), rhodium(IV) oxide        (RhO₂), and iridium(IV) oxide (IrO₂);    -   (c) amorphous nickel oxide nanoparticles and/or web; and/or    -   (d) conductivity enhancer nanoparticles selected from indium        oxide, ITO, and zinc oxide.

While the various embodiments are described with respect toelectrochromic windows, the embodiment methods, systems, and devices mayalso be used in materials for other types of smart windows. Such smartwindows may include, but are not limited to, polymer-dispersed liquidcrystals (PLDD), liquid crystal displays (LCDs), thermochromics, etc.

Robust Post-Tempering Electrodes

As discussed above, as part of the electrochromic device manufacturingprocess one or more layers of the device, including the crystallinenanostructure material of the working electrode 104, may be heattempered in an oven or furnace at temperatures ranging from 400 to 650°C. The heat tempering may last for 30-120 minutes, after which thelayers may be quenched or cooled. For example, quenching may includecooling the layers to temperatures under 100° C. using liquid or gas(e.g. water or air quenching) for periods on the order of seconds (e.g.5-15 seconds). In an example embodiment, the working electrode 104 mayinclude tungsten bronze nanoparticles (e.g. cesium doped tungsten oxide(e.g. CsWO_(3−X)) cubic nanoparticles and/or doped or undoped tungstenoxide (e.g. WO_(3−X)) hexagonal nanoparticles, in which X may be zero)and optionally amorphous niobium oxide (NbO_(X)) nanoparticles, whilethe counter electrode 108 may include cerium oxide nanoparticles andindium oxide nanoparticles. The electrochromic properties of the deviceshould remain the same or substantially the same after it has gonethrough the tempering process. However, during the tempering and heatquench process, sintering may occur in the working electrode, which maycause the nanoparticles to fuse, change its crystal structure or formnew crystal structures, or undergo undesirable phase transitions. Thesechanges to the nanoparticles may negatively affect the operation of theelectrochromic device.

For example, FIG. 2A shows a scanning electron microscope (SEM) image ofa sample of cubic cesium-doped tungsten oxide nanoparticles(specifically in FIG. 2A, Cs_(0.9)W₃O₉) that may be used in the workingelectrode 104 before tempering while FIG. 2B shows an SEM image of thesame sample after tempering at 650° C. After tempering, fusing of thenanoparticles and large crystal growth is clearly seen in the cubiccesium tungsten oxide sample in addition to the pre-existingnanoparticles. The new crystal growth seen in FIG. 2B may impedefunctioning of the sample within the working electrode 104 of anelectrochromic device.

Similarly, FIG. 2C shows a SEM image of a sample of hexagonalcesium-doped tungsten oxide nanoparticles (specifically in FIG. 2C,Cs_(0.2)WO₃) that may be used in the working electrode 104 beforetempering while FIG. 2D shows an SEM image of the same sample aftertempering at 650° C. After tempering, fusing of the nanoparticles andnew crystal growth is seen in the hexagonal cesium tungsten oxide samplein addition to the pre-existing nanoparticles. The new crystal growthseen in FIG. 2D may impede functioning of the sample within the workingelectrode 104 of an electrochromic device.

In contrast, FIGS. 3A and 3B show SEM images of a sample of ceria thinfilm (CeO₂) that may be used in the counter electrode 108 of anelectrochromic device before heat tempering (FIG. 3A) and after heattempering at 650° C. (FIG. 3B). As can be seen, the ceria thin filmremains relatively unchanged after the tempering process. FIG. 3C showspictures of ceria thin film after heat tempering in both bright and darkmode. As can be seen, the heat tempering does not lead to substantialchanges in the operation of the ceria thin film as a counter electrodein an electrochromic device.

Similarly, FIGS. 3D and 3E show SEM images of a sample of ITO thin filmthat may be used in the counter electrode 108 of an electrochromicdevice before heat tempering (FIG. 3D) and after heat tempering at 650°C. (FIG. 3E). As can be seen, the ITO thin film remains relativelyunchanged after the tempering process. Thus for some compositions of thecounter electrode 108, for example cerium oxide nanoparticles and/orindium oxide nanoparticles, no additional dopant or other materials areneeded to protect the counter electrode during the tempering process.

Various embodiments described herein provide for the incorporation ofvarious structures into nanocrystal structures, such as workingelectrodes in an electrochromic device, which may suppress undesirablenanoparticle crystallization, sintering, or phase transitions during theheat tempering process, or to promote desirable crystallization or phasetransitions. The structures may be compatible with a variety of metaloxide nanocrystals and amorphous metal oxide nanoparticles such as, butnot limited to, WO₃, CS_(x)WO₃, NbO_(x), TiO₂, MoO₃, NiO₂, and V₂O₅.

In some embodiments, sintering may be suppressed by the use ofcore-shell nanoparticles in which the shell material is a hightemperature stable material (i.e., stable at higher temperatures thanthe core material). A high temperature stable material may be a materialthat does not substantially crystallize and keeps the core material fromfusing at temperatures ranging from 100° C. to 700° C. An example of acore-shell nanoparticle 300 is shown in FIG. 4A. The core-shellnanoparticle 400 may be implemented in electrodes of the electrodesdevice, for example the working electrode 104. The core-shellnanoparticles 400 may be arranged, for example, in row configurationswithin the working electrode 104 so that ions in the electrolyte 106 maydiffuse into the working electrode 104.

The shell material 402 of the core-shell nanoparticle 400 may be, forexample, tantalum oxide (Ta₂O₅), or any other suitable high temperaturestable material (e.g. a metal oxide which is stable up to 700° C.) thatreduces or prevents core fusing with adjacent core-shell particles undertempering conditions. Even if the shell material 402 undergoes somesintering with other nanoparticle shells during the tempering process,the underlying core material 404 remains unchanged after temperingbecause it is protected by the shell material 402. The shell material402 may be composed of any metal, metal oxide, or other material thatallows diffusion of ions (e.g. lithium or other alkali or alkali earthions) between the core material 404 and the electrolyte 106. The shellmaterial 402 may also serve as an electron blocker (i.e. a low electronmobility layer). The shell material 402 may also serve as a coating forUV protection (e.g. also serve as protective layer 118).

The core material 404 may be any type of electrochemically activematerial, for example the materials discussed in relation to thecomposition of the working electrode 104. For example, the core material404 may include, among other things, cesium-doped tungsten oxide(CsWO_(3−x)) cubic crystalline structure nanoparticles, undopedhexagonal tungsten oxide (WO_(3−x)) nanoparticles, doped transitionmetal oxide bronze structures, and/or amorphous niobium oxide (NbO_(X))nanoparticles.

In an alternative embodiment, the tempering may promote a material phasechange may be favorable for device performance. For example, anelectrode material (e.g., nanoparticles or matrix) may be deposited onthe substrate in a first phase which may or may not have adequateelectrochromic properties, and after exposure to tempering conditions ittransitions to a second phase that has better electrochromic propertiesthan the first phase of the material. In some embodiments, theelectrochromic device may include amorphous niobium oxide (NbO_(X)),which may become crystalline niobium oxide (Nb₂O₅) during heat temperingand has a blue tint.

Alternatively to the spherical core-shell nanoparticle 400, othernon-spherical forms of nanoparticles may be used to reduce the degree offilm densification that may occur upon sintering. For example FIG. 4Bshows a nanoparticle-matrix composite layer 420 in which the matrixmaterial 422 forms a single flat matrix layer that separates individualnanoparticles of core material 424. The matrix material 422 may includetantalum oxide or any other suitable high temperature stable material(e.g. a metal oxide which is stable up to 700° C.). The core material424 may be any type of electrochemically active material, for examplethe materials discussed in relation to the composition of the workingelectrode 104. The nanoparticle-matrix composite layer 420 may be formedusing atomic layer deposition or through deposition of polyoxometalates.Other examples of non-spherical structures may include nanorods (e.g.bronze nanorods), porous web structures such as NbO_(X) web structuresused as a matrix, or polyoxometalate web or matrices. The workingelectrode 104 may in addition or alternatively contain dopants thatsuppress undesirable nanoparticle crystallization, sintering, or phasetransitions during the heat tempering process, or to promote desirablecrystallization or phase transitions. These various structures may alsoserve, or be combined with other materials to serve as the protectivelayer 118.

Use of the core-shell nanoparticle 400 or other materials or dopants toprevent sintering or other unwanted changes in the electrodes of anelectrochromic device during tempering may allow for large scaleproduction of electrochromic devices. Developing a material compositionand process condition that can maintain performance after themanufacturing process may also lead to lower cost products. Electrodescontaining materials that suppress undesirable nanoparticlecrystallization, sintering, or phase transitions during heat temperingmay enable deposition of liquid coatings on large form factor glasssubstrates, forming “jumbo” electrodes. For example, the jumboelectrodes may have dimensions of at least 4 feet by 4 feet, such as 8feet by 8 feet, 8 feet by 4 feet, 12 feet by 4 feet, 12 feet by 41 feetor 3.66 m by 12.5 m, or any other common dimensions for windows orform-factor glass substrates (e.g., up to 12 m by 18 m). These jumboelectrodes may then be shipped to third parties that may cut thesubstrates containing such electrodes to size, temper them, and assemblethe electrodes into various products. For example, the cut and temperedglass substrate containing the electrode may be assembled together witha counter electrode and an electrolyte into a dynamic glass pane. Thedynamic glass pane is then installed as an outer pane of glass in adouble pane window unit.

The jumbo electrodes may be shipped as flat planes, or may be flexibleand can be shipped in rolls. The ability to produce electrodes on jumbosized substrates may enable low cost of production of electrodes andelectrochromic devices, with more freedom in product sizes and shapes.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Thedescription was chosen in order to explain the principles of theinvention and its practical application. It is intended that the scopeof the invention be defined by the claims appended hereto, and theirequivalents.

The invention claimed is:
 1. An electrochromic device, comprising: aglass substrate; a working electrode disposed on the glass substrate andcomprising a high temperature stable material and nanoparticles of anelectrochromic active core material comprising doped or undoped tungstenoxide nanoparticles; a counter electrode comprising cerium oxidenanoparticles and indium oxide nanoparticles and that is stable attemperatures up to 700° C.; and an electrolyte deposited between theworking electrode and the counter electrode.
 2. The device of claim 1,wherein the high temperature stable material forms a sphericalnanoparticle shell around the nanoparticles of the electrochromic activecore material to form core-shell nanoparticles.
 3. The device of claim1, wherein the high temperature stable material forms a matrix aroundthe nanoparticles of the electrochromic active core material.
 4. Thedevice of claim 3, wherein the high temperature stable material forms asingle flat layer surrounding the core material.
 5. The device of claim1, wherein the high temperature stable material comprises tantalumoxide.
 6. The device of claim 1, wherein the core material comprisescesium doped tungsten oxide cubic nanoparticles and amorphous niobiumoxide nanoparticles.
 7. The device of claim 1, wherein the hightemperature stable material prevents fusing of the nanoparticles of theelectrochromic active core material at temperatures up to 700° C.
 8. Amethod of forming an electrochromic device, comprising: depositing aworking electrode onto a first substrate, wherein the working electrodecomprises a high temperature stable material and nanoparticles of anelectrochromic active core material comprising doped or undoped tungstenoxide nanoparticles; heat tempering the working electrode and the firstsubstrate, to change a phase of the electrochromic active core material;and depositing a counter electrode onto a second substrate, wherein thecounter electrode comprises cerium oxide nanoparticles and indium oxidenanoparticles and is stable at temperatures up to 700° C.
 9. The methodof claim 8, wherein the high temperature stable material forms aspherical nanoparticle shell around the nanoparticles of theelectrochromic active core material to form core-shell nanoparticles.10. The method of claim 8, wherein the high temperature stable materialforms a matrix around the nanoparticles of the electrochromic activecore material.
 11. The method of claim 10, wherein the high temperaturestable material forms a single flat layer surrounding the core material.12. The method of claim 8, wherein the high temperature stable materialcomprises tantalum oxide.
 13. The method of claim 8, wherein the corematerial comprises cesium doped tungsten oxide cubic nanoparticles andamorphous niobium oxide nanoparticles, and wherein changing the phase ofthe electrochromic active core material comprises changing the amorphousniobium oxide nanoparticles to crystalline niobium oxide nanoparticles.14. The method of claim 8, wherein the high temperature stable materialprevents fusing of the nanoparticles of the electrochromic active corematerial during the heat tempering.
 15. The method of claim 8, furthercomprising: heat tempering the counter electrode and the secondsubstrate; and forming an electrolyte between the working electrode andthe counter electrode.
 16. The method of claim 8, wherein the firstsubstrate is a jumbo glass substrate and the method further comprises:cutting the first substrate after depositing the working electrode ontothe first substrate; heat tempering the working electrode and the firstsubstrate at temperatures up to 700° C.; assembling the workingelectrode and the first substrate with a counter electrode and anelectrolyte into a dynamic glass pane; and providing the dynamic glasspane as an outer pane of glass in a double pane window unit.
 17. Themethod of claim 8, further comprising quenching the working electrodeand the first substrate to temperatures less than 100° C., wherein thequenching occurs over a period of seconds.